The invention relates to the field of electronic labels which are affixed on products in order to identify them according to their attributes and, more particularly, to a procedure for identifying the electronic labels of an ensemble on the basis of their estimated number.
It is known to use xe2x80x9cbarxe2x80x9d codes which are printed on products in order to identify them and which are read by an optical device during their passage through the check-out of a store. The bar code read makes it possible to interrogate a data-processing device which delivers, for example, the cost of the product.
These bar codes have certain limitations which are essentially due to the fact that they are frozen at the time that they are being printed and therefore cannot be modified during the life of the product.
Thus it has now been proposed to replace bar codes with labels called electronic labels which contain electronic circuits, such as a memory capable of writing an n-bit binary code. This binary code is representative of the bar code, especially for indicating the type of product, but can also represent other information or attributes capable of being modified during the life of the product assuming, of course, that the memory is rewritable for at least certain parts of the n-digit binary code. Thus, it may include the date of sale, the identification of the store, the term of the guarantee, the date of the end of the guarantee, etc.
The interrogation/read/write device may operate in the manner of a bar code read device, that is to say it communicates only with a single electronic label at a time, the one which is presented to it within its volume of radiation.
However, the interrogation/read/write device is capable of simultaneously interrogating all the electronic labels located within its volume of radiation so that these also respond simultaneously and thus cannot be identified from each other.
To solve this problem, it has been proposed to interrogate the electronic labels using various so-called anticollision procedures which make it possible to xe2x80x9cmanagexe2x80x9d the labels which respond simultaneously and which are therefore xe2x80x9cin collisionxe2x80x9d.
These anticollision procedures are divided into two classes, namely deterministic and nondeterministic.
In the first class, a first way of operating is to interrogate the electronic labels on the basis, for example, of all or part of the code for identifying the product until a single label responds to this code or part of a code. This first way may result in a high number of interrogations, recognizing that for a code containing n=64 bits, there are more than 1019 possibilities.
A second way of operating consists in making the interrogation/read/write device repeat that which it receives from the electronic labels and to do so bit by bit or block of bits by block of bits. The electronic labels which recognize the repeated bit or block of bits know that they have been taken into account by the interrogation device and continue alone to transmit another bit or block of bits. These operations are repeated until the selection of a single electronic label.
The deterministic procedures assume that there are not two electronic labels having the same identification code, which constitutes a major constraint if there is a large number of products of the same type, for example in a supermarket, as each article must be labeled differently in order to be recognized.
Furthermore, these deterministic procedures identify only the electronic labels which are presented at the start of implementation of the procedure for a given ensemble.
Any new label with respect to this ensemble cannot be taken into account and must wait for the next cycle of the identification procedure. As a result, these deterministic procedures are therefore not applicable to continuous identification of products, for example those moving along a conveyor belt.
In nondeterministic procedures, the electronic labels are designed to transmit a message after a time interval of random duration starting from an initial point given by the interrogation/read/write device. The electronic label will consider that its message has been recognized if it receives an acknowledgement from the interrogation/read/write device. In the absence of an acknowledgement, the unrecognized electronic label sends its message during the next interrogation cycle after the elapse of a new time interval of random duration.
In such a nondeterministic procedure, it is probable that several electronic labels transmit simultaneously if their total number is substantially greater than the number of random durations provided in one cycle, thereby confusing the message from the electronic label which was transmitted first.
Thus, it has been proposed to make the electronic labels silent upon detection of a transmission from another label, which detection may be performed by the electronic labels themselves or by the interrogation/read/write device.
The performance of nondeterministic procedures is determined by the maximum number Nsmax of windows of transmission duration during a cycle in relation to the number N of electronic labels, this number Nsmax also defining the number of possible random waiting periods. Thus, in the case of N electronic labels, the procedure is optimal for an Nsmax value of Ns1, but in the case of 2N electronic labels the procedure is optimal for an Nsmax value of 2Ns1. This has the consequence that the procedure is not suitable for any number of electronic labels.
Moreover, it is not possible to reliably detect two electronic labels which transmit exactly at the same moment. This may give rise to situations in which one electronic label thinks it has been identified by the acknowledgement, whereas the latter was intended for another electronic label.
One object of the present invention is therefore to implement a procedure of the nondeterministic type for identifying electronic labels affixed on products which makes it possible very rapidly to identify the electronic labels of an ensemble, whatever their number and their identifier.
This object is achieved by adapting the number of random waiting periods or transmission windows to the number of electronic labels remaining to be identified. This adaptation is achieved by the interrogation/read/write device on the basis of the identification results from the preceding cycle.
The invention relates to a procedure for identifying electronic labels affixed on products using an interrogation device, characterized in that it comprises the following steps consisting in:
(a) indicating to the electronic labels the number Ns of consecutive transmission windows of a first cycle or round;
(b) counting, during the cycle of Ns windows, the messages received from the electronic labels in order to determine the number ni of identifications, the number nv of blank spaces or windows and the number nc of collisions;
(c) stopping the procedure if nc=0 or passing to step (d) if ncxe2x89xa00;
(d) computing a number Ns1 of transmission windows for the next cycle on the basis of the values of Ns, ni, nv and nc; and
(e) returning to step (a) with Ns=computed Ns1.
The procedure furthermore includes, in each electronic label, the following steps consisting in:
(m) receiving the number Ns of windows at each cycle or round;
(n) randomly choosing a transmission window from Ns;
(o) transmitting a message during the period of the chosen window;
(p) waiting for a message originating from the interrogation/read/write device;
(q) receiving the acknowledgement of the message transmitted by the interrogation/read/write device in the absence of a collision; and
(r) returning to step (m) should there be no acknowledgement, that is to say in the event of a collision or blank window.